Wrong again.
The main reason is that every penny counts and they don't give a toss what problems the buyer will have; profit is the only motivator.
Combi Boiler size - does it matter?
- Thread starter jesteh
- Start date
The main reason is that every penny counts and they don't give a toss what problems the buyer will have; profit is the only motivator.
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C
commercialman
Just thought that I'd check back on this post again and it's a good job I did!
You don't just install the biggest boiler the customer can afford yet we must accept a modern HE boiler is very different kettle to the old coventional boiler (time to throw out your old myers calculator
)
Don't get me wrong some interesting points have been made reguarding sizing of boilers.
But for replacement boilers in UK houses and flats we should now use "The Whole House Boiler Sizing Method" for boiler sizing.
Just did a quick google and this is the 1st one that I found.
http://www.wessexwoodboilers.co.uk/pdfs/359782525_boiler_size.pdf
Servotech,
You don't just install the biggest boiler the customer can afford yet we must accept a modern HE boiler is very different kettle to the old coventional boiler (time to throw out your old myers calculator
)Don't get me wrong some interesting points have been made reguarding sizing of boilers.
But for replacement boilers in UK houses and flats we should now use "The Whole House Boiler Sizing Method" for boiler sizing.
Just did a quick google and this is the 1st one that I found.
http://www.wessexwoodboilers.co.uk/pdfs/359782525_boiler_size.pdf
Servotech,
Bet the customer won't be impressed with the time it will take to run a bath with a combi based on this method.
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No, It's not suitable for combi's or solid fuel boilers.
Safety!
There are certain safety issues with a solid fuel boiler that the worksheet makes no allowances for.
Servotech,
There are certain safety issues with a solid fuel boiler that the worksheet makes no allowances for.
Servotech,
So with regards to my question on here, this method of boiler sizing is irrelevant as I am getting a combi boiler.
In summary, combi boiler you need to work out flow rates you need. Regular boiler, you need to work out heat output.
Is that correct?
In summary, combi boiler you need to work out flow rates you need. Regular boiler, you need to work out heat output.
Is that correct?
As boilers have a huge modulation range these days, sizing to the closest possible match has no other purpose than saving a few bob by getting the smaller model for non-combis. This does of course eliminated the possibility of increasing the demand in the future.
For combi boilers, it has always been utterly pointless, unless you have a huge heat demand, and you want to see if the boiler is strong enough.
I know; but you are not comparing like for like.
The 5kW was for the heating only of a 3 bed mid-terrace house. While the 12kW and 15kW were for detached or semi-detached houses and included an allowance for the vented HW cylinder.
If you want true comparisons of the heat loss they are:
Mid-terrace - 4.94kW
Semi - 5.93kW
Detached - 6.81kW
Mr Google strikes again: "allowance for dhw"
The arrival of independent timers made the need for that allowance obsolete.
Down to 0.01 kWatt accurate
; how do I show that I am only talking about theories that I found on google, and never actually installed a boiler in a house in my life?From working as a RGI; quite a bit different than googling things from your armchair.
I could comfortably heat my house with a 5kW boiler, and it is detached. I dread to think how long a bath would take with a 5kW combi and a shower would be impossible. The old 27kW nominal (19kW output) combi I used to have was just about OK both for shower and bath and very few people would be happy with anything less powerful.
The modern trend for every more powerful hot water supplies with better insulated houses (plus low flow temperatures, weather compensation, and TRVs) means that combis frequently don't modulate down low enough. A 30kW combi might modulate to 6-8KW but typical heating needs 90% of the time will be less than half that. The 35+kW combis that are now almost the norm modulate to around 10kW which is way higher than most modern houses can use. Just have to deal with it, not the end of the world.
The modern trend for every more powerful hot water supplies with better insulated houses (plus low flow temperatures, weather compensation, and TRVs) means that combis frequently don't modulate down low enough. A 30kW combi might modulate to 6-8KW but typical heating needs 90% of the time will be less than half that. The 35+kW combis that are now almost the norm modulate to around 10kW which is way higher than most modern houses can use. Just have to deal with it, not the end of the world.
At last, someone who does not have preconceived ideas!
I agree; but I was not suggesting a 5kw combi boiler.
Music to my ears!
I assume you mean BenG and all the other Luddites who have not moved with the times.
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